This invention relates to helical products and methods of making such products.
U.S. Pat. No. 5,927,125 describes methods and apparatus for manufacturing helical products and provides a discussion of earlier methods of making such products. The present application relates to particular products that can be made in helical form and discusses methods of using or adapting the apparatus and methods of U.S. Pat. No. 5,927,125 to making such products.
Helical devices as shown in U.S. Pat. No. 5,927,125 have some minor drawbacks. The first is that the free end of the helix can dig into optical cables when the cables are under tension and this is undesirable due to the relatively fragile nature of optical cables. The second drawback is that once the helical device is in place about a cable, whether optical or otherwise, it is difficult to get the free end of the helix away from the cable to unwind the helix. It is known with wire helical devices to flare the ends of a helix by forming the helix and then manually flattening its end in a press but, so far as the applicants are aware, such a method has not been used for metal strip helical devices.
GB 2303503 discloses, in the drawings only, flared ends to the helical strips. There is no disclosure as to the nature of this flaring nor as to how such flaring may be made.
GB 2308752 arguably shows a flared end to a helical unit. There is no disclosure as to the nature of the flaring end nor is there any disclosure as to the material of the helical unit.
GB 2234830 discloses a spiral helix used as a damper in which the helix xe2x80x9chas an overall diameter which increases smoothly towards this endxe2x80x9d.
In a first aspect, the present invention provides a helical device for engagement with a cable, the helical device comprising a single length of metal strip comprising a first helical section, a second non-helical section, and a third helical section, the end of either or both the first and third helical sections remote the second helical section being flared away from the longitudinal axis of the helix, the flaring being in the form of a section of spiral helix form.
The inner surface of the helical sections may be knurled and it is advantageous that the knurling occupy only a part of the width of the strip material leaving the edges essentially free of knurling.
To produce these devices one may follow the steps of:
i) feeding strip material to an apparatus;
ii) within the apparatus automatically activating helix forming mean to form a first section of the strip material into the shape of a helix;
iii) within the apparatus automatically inactivating the helix forming means so as not to form a second section of the strip material into the shape of a helix;
iv) within the apparatus automatically activating the helix forming means to form the third section of the strip material into the shape of a helix;
v) selectively controlling the helix forming means to produce between helical sections of adjacent devices sections of increasing and then decreasing diameter, the strip being cut between the sections of increasing and then decreasing diameter, either prior or subsequent to the formation of the section of decreasing diameter, to provide the flared ends of the two adjacent devices; and
vi) repeating steps i) to v) to produce further devices.
Further features of the invention will be apparent from the following description and the claims.